Power supplies such as batteries or transformer rectifier systems with associated means to control the power supplied to the motor of model railway locomotives are well known. In their simplest forms they consist of a source of electrical energy which supplies current to the motor through a variable resistance in order to regulate the speed. This means of controlling speed however is very poor as it is essentially a constant current device. Increasing loads on the motor reduce its speed for a given speed setting and inasmuch as the frictional effects of motor brushes, bearings and gears are a large erratic load at low speeds it is almost impossible to run such devices slowly.
A better method of control is to use a variable ratio or autotransformer to supply the energy to the motor. This holds a constant voltage to the motor and as the load increases the motor torque also rises. Other systems such as shown in U.S. Pat. Nos. 3,855,511 or 3,422,331, control the armature current as a function of load. These basic control methods are used in such power supplies today. Slow speed operation is still very poor in model railway systems using such speed controls, however, due to the highly erratic frictional loads which predominate at low armature speeds. Furthermore, acceleration, deceleration and braking conditions are not available to simulate action of trains.
Braking has been accomplished in prior art transistorized model locomotive power supplies by connecting a resistor and large capacitor in the armature current supply circuit, so that the charge is drained off the capacitor thereby slowing the motor speed when the current supply is switched off. However, this type of braking is not the same as in standard railroad practice, where air is admitted to the brake cylinders by means of a hand valve and the longer the valve is held open, the greater the braking effect. Thus, if the valve were to be held open the brakes would soon lock the wheels.